Thermodynamics of black holes reveals that geometrical quantities
such as horizon area and surface gravity are related to the
thermodynamic quantities such as entropy and temperature. The
first law of black hole thermodynamics implies that the entropy
and the temperature together with the energy (mass) of the black
hole satisfy \(dE=TdS\)  [1]}. In 1995 Jacobson [2]}
put forwarded a new step and suggested that the hyperbolic second
order partial differential Einstein equation for the spacetime
metric has a predisposition to thermodynamic behavior. He
disclosed that the Einstein field equation is just an equation of
state for the spacetime and in particular it can be derived from
the proportionality of entropy and the horizon area together with
the fundamental relation \(\delta Q=TdS\) . Following Jacobson,
however, several recent investigations have shown that there is
indeed a deeper connection between gravitational dynamics and
horizon thermodynamics. The deep connection between horizon
thermodynamics and gravitational dynamics, help to understand why
the field equations should encode information about horizon
thermodynamics. These results prompt people to take a statistical
physics point of view on gravity.
